Abstract

To ensure safe driving an accurate mental representation of the current traffic situation is required. This representation is the result of a comprehension process that can be impaired by in-car tasks that visually and / or cognitively distract the driver. To minimize distraction from in-car tasks and the resulting negative effects on the driver’s situation representation, in-car devices and the tasks associated with them have to be carefully designed. To achieve a design with both minimal visual and cognitive demands, measurement procedures are required that allow assessment of the visual and cognitive demands of these in-car devices and tasks. The aim of this research project was to test a specific secondary-task procedure as a method of simultaneously evaluating the visual and cognitive demands of in-car tasks. Two experiments and their results are presented.
The first experiment tested the secondary-task procedure. Subjects performed three in-car tasks that differed in their visual and / or cognitive demands. The in-car tasks were performed as the primary task. The n-back task (Owen et al. 2005) was introduced as a secondary task. In this task participants are presented with a series of stimuli and their task is to decide whether the current stimulus is the same as the stimulus presented n trials before. In the experiment n was set to 1 meaning that the participants had to compare the current stimulus with the previous one. The task yields two measures that are supposed to allow assessment of both the visual and cognitive demands of the primary task. First, the detection rate was measured as an estimate of the visual demand of the task. It is the proportion of visual stimuli subjects responded to, irrespective of the correctness of the response. If the primary task is highly visually demanding the participant will simply miss many of the visual stimuli. The proportion of correct responses of all given reactions, the hit rate, was used as a measure of the cognitive demands of the primary task. If the in-car task is highly cognitively demanding the participant may often forget the previous stimulus or may frequently fail to encode the
current stimulus for comparison with the next one. This should lead to more false responses to the stimuli. The results indicate that the detection rate can be used as a valid measure of a task’s visual demand. Our findings also showed that detection rates are influenced by a high cognitive demand of an in-car task. At least, the influence of cognitive demand on the detection rate was much smaller than the influence of visual demand. Results for the hit rate were not as clear as with the detection rate.
The aim of the second driving simulator experiment was to examine the effects of the in-car tasks on situation awareness and to compare these effects with the effects these tasks had on the detection and the hit rate of the 1-back task. First, we expected that highly visually demanding tasks, leading to a low detection rate in Experiment 1, should interfere with the perception of relevant information. An incomplete situation model should be the consequence. Second, highly cognitively demanding tasks, associated with a low hit rate in Experiment 1, should interfere with the maintenance of the situation model. Situation awareness was measured by a freezing-procedure. The driving simulation was interrupted several times and the driver was asked about the number of cars in different lanes. The results showed, in accordance with the predictions, a decrease in response accuracy for the rear traffic when cognitively demanding tasks were performed while driving. These tasks seemed to interfere with the maintenance of the situation model. But from the perspective of using the 1-back task as a measurement procedure for cognitive demand, the differentiation between tasks was not optimal. Here future research is necessary on how to improve the procedure. Contrary to the predictions, the visually demanding task did not interfere with maintaining the situation model for the traffic situation in front of the vehicle. It seems that the visual demand of the 1-back task is much greater than visually checking the traffic situation in front. However, it may be advantageous to use the 1-back task during the design phase, as it would ensure that only those designs with low visual demand are developed for use in cars.
Practical relevance
In recent years different telematic systems have been increasingly offered as basic equipment in new cars. These systems have to be designed in such a way as to not distract the driver while driving. This paper introduces a simple procedure, based on a well-known experimental psychology paradigm, that allows an evaluation of the systems’ safety-critical visual and / or cognitive demand early in their developmental process.